Capture of hydrogen boiloff

ABSTRACT

A hydrogen boiloff capture system. The hydrogen boiloff capture system having a cryogenic tank for storing liquid hydrogen. The hydrogen boiloff capture system also includes an intermediate tank fluidically coupled with the cryogenic tank. The intermediate tank is configured to receive hydrogen gas boiloff from the cryogenic tank. The intermediate tank is further configured to provide the hydrogen gas boiloff to a lighter-than-air craft to regulate buoyancy of the lighter-than-air craft. The intermediate tank is also configured to provide the hydrogen gas boiloff to a hydrogen fuel cell coupled to the lighter-than-air craft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is claims priority to and is a continuation-in-part ofU.S. patent application Ser. No. 17/804,299 filed on May 26, 2022,entitled “LIGHTER-THAN-AIR CRAFT WITH HYDROGEN PROPULSION” by Miftakhovet al, assigned to the assignee of the present application, havingAttorney Docket No. ZEAV-001, the disclosure of which is hereinincorporated by reference in its entirety.

The application Ser. No. 17/804,299 claims priority to and the benefitof co-pending U.S. Provisional Patent Application No. 63/262,495, filedon Oct. 14, 2021, entitled “LIGHTER-THAN-AIR CRAFT WITH HYDROGENPROPULSION” by Miftakhov et al., and assigned to the assignee of thepresent application, the disclosure of which is hereby incorporatedherein by reference in its entirety.

This application also claims priority to and the benefit of co-pendingU.S. Provisional Patent Application No. 63/262,495, filed on Oct. 14,2021, entitled “LIGHTER-THAN-AIR CRAFT WITH HYDROGEN PROPULSION” byMiftakhov et al., and assigned to the assignee of the presentapplication, the disclosure of which is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention pertains to lighter-than-air (LTA) craft, liftinggases for LTA craft and the capture of hydrogen boiloff.

BACKGROUND

The term “LTA craft” refers to several types of aircraft which, at leastpartially, utilize a lighter-than-air gas to produce lift. LTA craftinclude, but are not limited to, steerable LTA craft, dirigibles,blimps, rigid airships, semi-rigid airships, Zeppelins, hybrid airships,and the like. Steerable LTA craft and dirigibles generally refer to anyLTA craft which is powered and steerable. Blimps are LTA craft having anouter envelope whose shape or physical configuration is maintained bythe internal pressure of the lifting gas confined within the envelope.Unlike blimps, semi-rigid and rigid LTA craft have a framework which atleast partially defines the shape or configuration of the envelope ofthe LTA craft. Zeppelins refer to a particular type of rigid LTA craftproduced by the Luftschiffbau Zeppelin company of Germany. Hybrid LTAcraft produce lift using a combination of lighter-than-air gas and anaerodynamic feature such as, for example, a wing or a rotor.

LTA craft have significant utility as lifting vehicles, passengertransports, research tools, and numerous other applications. LTA crafthave, in the past, been considered such an essential mode of air travelthat the spire of the Empire State building was originally built andintended for use as a mast to moor LTA craft. Several infamous incidentswith LTA craft, which utilized highly flammable lifting gases, found LTAcraft losing favor among the general population as passenger transportvehicles. Despite such incidents, LTA craft remain an important andvaluable tool in the field of modern aeronautics.

In various applications, liquid hydrogen is cryogenically stored.Sustained cryogenic storage of liquid hydrogen typically requires theuse of durable storage tanks under very high pressures (5000-10,000 psistorage tank pressure), and/or insulation of the durable storage tank,and/or some form of active cooling. Such mechanisms for sustainedcryogenic storage have an intrinsic weight penalty associated therewith.Specifically, durable storage tanks are heavy, and the insulation oftenused in conjunction with the durable storage tanks further compounds theweight penalty associated with cryogenic storage of liquid hydrogen.Additionally, any active cooling system will inherently increase theweight penalty corresponding to the use of conventional mechanisms forsustained cryogenic storage of liquid hydrogen. As a result of theweight penalty, conventional cryogenic storage mechanisms for liquidhydrogen are not well suited for use in LTA craft and other aircraftwhere increases in weight are highly undesirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe Description of Embodiments, illustrate various embodiments of thesubject matter and, together with the Description of Embodiments, serveto explain principles of the subject matter discussed below. Unlessspecifically noted, the drawings referred to in this Brief Descriptionof the Drawings should be understood as not being drawn to scale.Herein, like items are labeled with like item numbers.

FIG. 1 is a schematic diagram of a lighter-than-air (LTA) craft having ahydrogen fuel cell and a propulsion system coupled thereto, inaccordance with embodiments of the present invention.

FIG. 2 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes ahydrogen-containing compartment surrounded by a volume of helium, inaccordance with embodiments of the present invention.

FIG. 3 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a componentfor altering the concentration of hydrogen in the helium and hydrogenmixture comprising a lifting gas, in accordance with embodiments of thepresent invention.

FIG. 4 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a heatexchange component, in accordance with embodiments of the presentinvention.

FIG. 5 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a heatexchange component, in accordance with embodiments of the presentinvention.

FIG. 6 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a heatexchange component coupled with a buoyancy adjustment feature, inaccordance with embodiments of the present invention.

FIG. 7 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a heatexchange component coupled with a buoyancy adjustment feature, inaccordance with embodiments of the present invention.

FIG. 8 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a pluralityof regions disposed within its enclosure, in accordance with embodimentsof the present invention.

FIG. 9 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a pluralityof regions disposed within its enclosure, in accordance with embodimentsof the present invention.

FIG. 10 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes a pluralityof regions disposed within its enclosure, in accordance with embodimentsof the present invention.

FIG. 11 is a schematic diagram of another embodiment of the presentinvention in which a lighter-than-air (LTA) craft includes one or moresensors and/or a hydrogen scavenging component, in accordance withembodiments of the present invention.

FIG. 12 is a schematic diagram of a lighter-than-air (LTA) craft havinga cryogenic tank, an intermediate tank, a hydrogen fuel cell and apropulsion system coupled thereto, in accordance with embodiments of thepresent invention.

FIG. 13 is a schematic diagram of a heavier-than-air craft having acryogenic tank and an intermediate tank which are coupled to a hydrogenfuel cell and a propulsion system, in accordance with embodiments of thepresent invention.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to various embodiments of thesubject matter, examples of which are illustrated in the accompanyingdrawings. While various embodiments are discussed herein, it will beunderstood that they are not intended to limit to these embodiments. Onthe contrary, the presented embodiments are intended to coveralternatives, modifications and equivalents, which may be included inthe spirit and scope of the various embodiments. Furthermore, in thisDescription of Embodiments, numerous specific details are set forth inorder to provide a thorough understanding of embodiments of the presentsubject matter. However, embodiments may be practiced without thesespecific details. In other instances, well known methods, procedures,components, and circuits have not been described in detail so as not tounnecessarily obscure aspects of the described embodiments.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “an embodiment,” “various embodiments,” “someembodiments,” or similar term(s) means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, the appearances of suchphrases in various places throughout this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics of any embodimentmay be combined in any suitable manner with one or more other features,structures, or characteristics of one or more other embodiments withoutlimitation.

Although one or more embodiments of the present invention have beendescribed in some detail for clarity of understanding, it will beapparent that certain changes and modifications may be made within thescope of the various embodiments. Accordingly, the described embodimentsare to be considered as illustrative and not restrictive, and the scopeof the various embodiments is not to be limited to details given herein,but may be modified. In the various embodiments, elements and/or anydescribed steps do not imply any particular order of operation, unlessexplicitly stated therein.

As an overview, LTA craft have, in the past, utilized various flammablelifting gases for buoyancy. Due to the inherent risks associated withthe use of flammable lifting gases, many flammable lifting gases are nowconsidered far too dangerous for use in LTA craft. Hydrogen, forexample, has long been deemed unsuitable for use as a lifting gas in LTAcraft. As an example, hydrogen has been completely abandoned for use asa lifting gas in passenger LTA craft since the late 1930s. As will bedescribed in detail below, embodiments of the present invention providea novel lifting gas which includes components currently dismissed as toodangerous for use in LTA craft. Additionally, below describedembodiments of the present invention will uniquely and advantageouslyutilize the currently dismissed lifting gas component as a power sourcefor the LTA craft.

With reference now to FIG. 1 , a schematic diagram of an LTA craft 100in accordance with an embodiment of the present invention is shown. LTAcraft 100 of the present embodiment includes an envelope 102 whichsurrounds and confines a lifting gas 114. Although graphically depictedas 114, it will be understood that in some embodiments of the presentinvention, lifting gas 114 will occupy the entirety of the availablevolume enclosed within envelope 102. Additionally, lifting gas 114 willbe described in detail below. LTA craft 100 further comprises a supplyline 104 which fluidically couples lifting gas 114 disposed withinenvelope 102 with a hydrogen fuel cell 106. Referring still to LTA craft100, an electrical supply line 108 is shown electrically couplinghydrogen fuel cell 106 with a propulsion system 109 comprised of motor110 and propeller 112. Although propulsion system 109 of LTA craft 100is comprised of motor 110 and propeller 112, embodiments of the presentinvention are well suited to use with a predominantly-electricpropulsion system comprised of components other than motor 110 andpropeller 112. A propulsion system may be understood to comprise a meansof providing thrust in any direction.

With reference still to FIG. 1 , it should be noted that, for purposesof brevity and clarity, LTA craft 100 of the present embodiment mayinclude various other components not depicted in FIG. 1 or described inthe present specification. Such components can include, but are notlimited to, a cockpit, passenger seating, hoisting mechanisms, mooringdevices, and the like. Furthermore, it should be noted that the variousembodiments described herein are well suited to use with numerous typesof LTA craft including, but not limited to, steerable LTA craft,dirigibles, blimps, rigid airships, semi-rigid airships, Zeppelins,hybrid airships, and the like.

Referring now to lifting gas 114 of FIG. 1 , in one embodiment of thepresent invention, lifting gas 114 is comprised of helium and hydrogengas. As stated previously, hydrogen has long been deemed unsuitable foruse as a lifting gas in LTA craft due to the flammability of hydrogen.In the present embodiment, lifting gas 114 is comprised of a mixturewherein the percent by volume of hydrogen does not exceed approximately4 percent. As hydrogen has a lower explosive limit (LEL) ofapproximately 4 percent by volume in air, embodiments of the presentinvention advantageously provide a hydrogen-containing lifting gas whichdoes not suffer from the flammability concerns previously associatedwith conventional hydrogen lifting gases. In another embodiment, liftinggas 114 is comprised of a mixture wherein the percent by volume ofhydrogen does not exceed a percentage such that when lifting gas 114escapes to an environment where sufficient oxygen for combustion ispresent and mixes to form a local mixture, the percent by volume ofhydrogen in the local mixture does not exceed the LEL at any point. As aresult, lifting gas 114 of the present embodiment is nonflammable duringoperating conditions for LTA craft 100. For purposes of the presentApplication, the phrase “operating conditions for LTA craft” refers tofueling, pre-flight activities, take-off, flight, in-flight operationsof all types, mooring, landing, unloading, disembarking, storing of theLTA craft, and any other activities associated with an LTA craft of anytype.

Referring still to lifting gas 114 of FIG. 1 , in one embodiment of thepresent invention, lifting gas 114 is a mixture of helium and hydrogenwherein helium comprises approximately 96 percent by volume of themixture and hydrogen comprises approximately 4 percent by volume of themixture. Using, as an example, an LTA craft having 360,000 cubic feet oflifting gas capacity, lifting gas 114 of the present embodiment would becomprised of approximately 14,400 cubic feet of hydrogen andapproximately 345,600 cubic feet of helium.

Helium has a gross lifting force of approximately 60 pounds per 1,000cubic feet at standard temperature and pressure of 32 degrees Fahrenheitand 1 atmosphere. Hydrogen has a gross lifting force of approximately 68pounds per 1,000 cubic feet at standard temperature and pressure. As aresult, in the aforementioned LTA craft having a lifting gas capacity of360,000 cubic feet, a conventional helium lifting gas would produce21,600 pounds of gross lifting force. In an embodiment of the presentinvention in which lifting gas 114 comprises approximately 96 percent byvolume of helium and approximately 4 percent by volume of hydrogen, thesame LTA craft with the same lifting gas capacity of 360,000 cubic feetproduces just over 21,715 pounds of gross lifting force. Thus, in theexample provided, lifting gas 114 of the present embodiment providesover 115 pounds of additional gross lifting force. Further, lifting gas114 of the present embodiment achieves the aforementioned increasedlifting force while maintaining the nonflammable safety characteristicsof less effective conventional lifting gases.

Additionally, lifting gas 114 of FIG. 1 has other significant advantagesover conventional lifting gases. As one example of such advantages,lifting gas 114 of the present embodiment weighs less than conventionalhelium lifting gases. At standard temperature and pressure, helium has aweight of approximately 11 pounds per 1000 cubic feet. Hydrogen has aweight of approximately 5 pounds per 1000 cubic feet at standardtemperature and pressure. Hence, using the same example of an LTA crafthaving a lifting gas capacity of 360,000 cubic feet, a conventionalhelium lifting gas would weigh approximately 3,960 pounds. Lifting gas114 of the present embodiment weighs approximately 3,873 pounds. Hence,lifting gas 114 of the present embodiment beneficially weighsapproximately 87 pounds less than the conventional helium lifting gas.Moreover, taking the increased gross lifting force, approximately 115pounds, in combination with the decreased lifting gas weight,approximately 87 pounds, lifting gas 114 of the present embodimentprovides an overall increased lifting capacity of more than 200 lbs.Again, lifting gas 114 of the present embodiment provides such improvedlifting performance while maintaining the nonflammable safetycharacteristics of less effective conventional lifting gases.

As yet another example of the advantages of lifting gas 114 of thepresent embodiment, lifting gas 114 is less expensive than conventionalhelium lifting gases, and does not share their scarcity/non-renewabilityconcerns. At present, helium costs approximately $120 per 1000 cubicfeet. Furthermore, the cost of helium has risen sharply over recentyears and continues to rise. In fact, since approximately 2010, the costof helium has increased 10-30 percent each year. Hydrogen costsapproximately $4.25 per 1000 cubic feet. Returning to the above example,for 360,000 cubic feet, lifting gas 114 of the present embodiment isapproximately $1666 less expensive than a conventional helium liftinggas.

With reference again to FIG. 1 , a further significant advantage oflifting gas 114 is illustrated. As stated above, in embodiments of thepresent invention, LTA craft 100 comprises supply line 104 whichfluidically couples hydrogen fuel cell 106 and lifting gas 114. As aresult, in embodiments of the present invention, not only does liftinggas 114 provide buoyancy for LTA craft 100, lifting gas 114 alsoprovides a suitable hydrogen source for hydrogen fuel cell 106. Asdescribed above, in an LTA craft having 360,000 cubic feet of liftinggas capacity, lifting gas 114 of the present embodiment (i.e.,approximately 4 percent hydrogen by volume and approximately 96 percenthelium by volume) is comprised of 14,400 cubic feet of hydrogen and345,600 cubic feet of helium. Hence, lifting gas 114 of the presentembodiments provides a significant supply of hydrogen for hydrogen fuelcell 106. A related significant advantage is avoiding the need for afuel tank to hold compressed or liquid hydrogen as a fuel supply for afuel cell. Hydrogen tanks are generally assumed to be necessary for fuelcell-powered craft even though they raise cost and reduce performancethrough their significant added weight.

Referring still to FIG. 1 , it should be noted that hydrogen fuel cell106 is comprised of any type of hydrogen fuel cell which utilizeshydrogen and oxygen (the oxygen obtained, for example, from thesurrounding air) to generate electricity. It should further be noted, aswill be discussed in detail below, that a hydrogen fuel cell, such ashydrogen fuel cell 106, typically also produces heat and water duringthe exothermic process of generating electricity. As stated above, inthe example of an LTA craft having 360,000 cubic feet of lifting gascapacity, lifting gas 114 of the present embodiment is comprised of14,400 cubic feet of hydrogen. In a hydrogen fuel cell such as, forexample, a Polymer Electrolyte Membrane (PEM) hydrogen fuel cell,approximately 30 cubic feet of hydrogen is used per kilowatt hourgenerated by the hydrogen fuel cell. As lifting gas 114 of the presentexample includes 14,400 cubic feet of hydrogen, lifting gas 114 enablesthe generation of up to 480 kilowatt hours of energy by hydrogen fuelcell 106.

Referring still to LTA craft 100 of FIG. 1 , in embodiments of thepresent invention electrical supply line 108 electrically coupleshydrogen fuel cell 106 with propulsion system 109. As stated above,although propulsion system 109 of LTA craft 100 is comprised of motor110 and propeller 112, embodiments of the present invention are wellsuited to use with a propulsion system comprised of components otherthan motor 110 and propeller 112, for example many variants of electricpropulsion including one or more of a ducted fan, ion drive, directedthrust, tilted lift system, and propeller. In various embodiments of thepresent invention, propulsion system 109 will further comprise a batteryor other electricity storage device, not shown, for storing electricitygenerated by hydrogen fuel cell 106. Hence, in some embodiments of thepresent invention, electricity generated by hydrogen fuel cell 106 isprovided to propulsion system 109 using electrical supply line 108, andthe generated electricity is used to directly power, for example, motor110 to drive propeller 112. In other embodiments, electricity generatedby hydrogen fuel cell 106 and/or stored in an electricity storage deviceis provided to electrical components of LTA craft including, forexample, air conditioning, avionics, control systems, and lighting.

Referring again to FIG. 1 , in various other embodiments of the presentinvention, electricity generated by hydrogen fuel cell 106 is providedto propulsion system 109, using electrical supply line 108, and thegenerated electricity is stored, for example in a battery, forsubsequent and/or simultaneous use by propulsion system 109. Suchsimultaneous use may occur, for example, during periods of greater powerdemand or need from propulsion system 109. Further, embodiments of thepresent invention are well suited to use with various combinations ofdirect/immediate use of electricity generated by hydrogen fuel cell 106and storage/deferred use of electricity generated by hydrogen fuel cell106.

With reference next to FIG. 2 , another embodiment of the presentinvention is shown in which LTA craft 200 is comprised of envelope 102and in which the lifting gas is comprised of a compartment 202 disposedwithin envelope 102. In the present embodiment, compartment 202 containsa volume of hydrogen. In the embodiment of FIG. 2 , envelope 102 furthercontains a volume of helium 206 wherein volume of helium 206 is disposedsurrounding compartment 202.

In the embodiment of FIG. 2 , the ratio of volume of hydrogen 204 incompartment 202 with respect to the surrounding volume of helium 206 isdefined such that if the entirety of the volume of hydrogen 204 and thevolume of helium 206 are combined to form a mixture, the mixture isnonflammable during operating conditions for LTA craft 200. That is, inthe embodiment of FIG. 2 , should even the entirety of the volume ofhydrogen 204 in compartment 202 leak into, or otherwise mix with, thesurrounding volume of helium 206, the mixture would be comprised ofapproximately 96 percent by volume of helium and no more thanapproximately 4 percent by volume of hydrogen. Hence, as with liftinggas 114 of the embodiment of FIG. 1 , the embodiment of FIG. 2 ensuresthat, even under the scenario wherein all the hydrogen confined incompartment 202 mixes with the surrounding helium, the presentembodiment would still provide a hydrogen-containing lifting gas whichdoes not suffer from the flammability concerns previously associatedwith conventional hydrogen lifting gases.

With reference still to FIG. 2 , in one embodiment of the presentinvention compartment 202 is a rigid compartment. In other embodimentsof the present invention, compartment 202 is a non-rigid compartmentcapable of expanding and/or contracting based upon the pressure and/oramount of hydrogen contained therein. Furthermore, in variousembodiments of the present invention, compartment 202 is fillable withthe desired amount of hydrogen without requiring substantial compressionof the hydrogen. In one such embodiment compartment 202 may be evacuatedprior to introduction of hydrogen and/or compartment 202 easily expandsto mitigate significant compression of the introduced hydrogen. Byeliminating the need to significantly compress the hydrogen, embodimentsof the present invention advantageously enable compartment 202 to befilled rapidly and without the generation of heat caused by thecompression of the hydrogen. This or the embodiment described in FIG. 1will permit much more rapid refueling of the LTA craft than aconventional LTA whose hydrogen fuel is stored as compressed gas orliquid.

Still referring to FIG. 2 , LTA craft 200 further includes a hydrogensupply line 208 coupled to supply line 104. In so doing, embodiments ofthe present invention fluidically couple hydrogen fuel cell 106,compartment 202 and volume of hydrogen 204 disposed within compartment202. As a result, various embodiments of FIG. 2 supply hydrogen fuelcell 106 with, in some instances, substantially pure hydrogen. Thegeneration of electricity and use and/or storage of the generatedelectricity can occur as described above in conjunction with theembodiments of FIG. 1 . It should be noted that in various embodiments,supply line 104 and hydrogen supply line 208 are much more robust than,for example, envelope 102 thereby further mitigating the potentialdamage to supply line 104 or hydrogen supply line 208 and any potentialleakage of hydrogen from supply line 104 or hydrogen supply line 208.

With reference next to FIG. 3 , another embodiment of the presentinvention is shown in which an LTA craft 300 includes a component 302(coupled with supply line 104) for altering the concentration ofhydrogen in the helium and hydrogen mixture comprising lifting gas 114.Moreover, in the present embodiment, component 302 alters theconcentration of hydrogen prior to utilization of lifting gas 114 byhydrogen fuel cell 106. In various embodiments of the present invention,the hydrogen and helium comprising lifting gas 114 are at leastpartially separated from each other by component 302. Hence, component302 effectively alters the concentration of hydrogen prior toutilization of lifting gas 114 by hydrogen fuel cell 106. In someembodiments, component 302 increases the ratio of hydrogen to helium inthe mixture prior to utilization by hydrogen fuel cell 106. It should benoted that embodiments of the present invention are well suited tooperation without component 302 since fuel cell 106 may operate onhydrogen mixed with other gases such as helium, outputting a mixturewith less hydrogen. The other gasses, depleted of hydrogen, may bereturned to the chamber 114, for example by a return line 303 whichfluidically couples fuel cell 106 and envelope 102. As stated above, itshould be noted that in various embodiments, supply line 104 and/orreturn line 303 are much more robust than, for example, envelope 102thereby further mitigating the potential damage to supply line 104and/or return line 303 and any potential leakage of hydrogen from supplyline 104 and/or return line 303.

With reference again to FIG. 3 , in one embodiment, component 302 iscomprised, for example, of a palladium-based alloy. Such palladium-basedalloys include, but are not limited to palladium alloyed with refractorymetals such as, for example, niobium, molybdenum, ruthenium, tantalum,tungsten, rhenium, vanadium and the like. Further, in variousembodiments of the present invention, component 302 may include, inaddition to or in lieu of the above-described materials, low-meltingmetals such as, but not limited to, lithium, magnesium, indium, lead,tin, bismuth and the like. Additionally, in various embodiments of thepresent invention, such palladium alloys comprising component 302 areformed into high plasticity, micron-sized palladium-alloy foils andtubes. It should be noted that embodiments of the present invention arewell suited to having component 302 be comprised of various othermaterials and/or structures capable of altering the concentration ofhydrogen prior to utilization of lifting gas 114 by hydrogen fuel cell106.

Referring still to FIG. 3 , in various embodiments of the presentinvention, a return line 304 fluidically couples component 302 andenvelope 102. In various embodiments, return line 304 is used to return,for example, helium separated from lifting gas 114 by component 302 towithin envelope 102. It should be noted that in various embodimentsreturn line 304 is used to return, for example, a mixture of helium andhydrogen, after interaction with component 302, to within envelope 102.

With reference next to FIG. 4 , another embodiment of the presentinvention is shown in which an LTA craft 400 includes a heat exchangecomponent 402 fluidically coupling hydrogen fuel cell 106, envelope 102,and lifting gas 114 disposed within envelope 102. As stated above, ahydrogen fuel cell, such as hydrogen fuel cell 106, typically alsoproduces heat and water during the exothermic process of generatingelectricity. In the present embodiment, said heat exchange componentprovides a flow path for heat, generated by hydrogen fuel cell 106, tobe provided to, and/or directly inside of, envelope 102 to adjust thetemperature of lifting gas 114. In the embodiment of FIG. 4 , heatgenerated by hydrogen fuel cell 106 travels along path 403 of heatexchange component 402 and along path 402 a of heat exchange component402 to, and/or through, envelope 102 to alter the temperature of liftinggas 114. It will be understood that altering the temperature of liftinggas 114 can be advantageously used to, in turn, alter the buoyancyprovided by lifting gas 114, which may be used to compensate for theloss of lifting force from the hydrogen consumed by fuel cell 106. Invarious other embodiments, heat generated by hydrogen fuel cell 106travels along one or more of paths 402 b and 402 c (in addition to, orin lieu of travelling along path 402 a) of heat exchange component 402to alter the temperature of hydrogen fuel cell 106 and/or lifting gas114 prior to utilization by hydrogen fuel cell 106. It will beunderstood that altering the temperature of hydrogen fuel cell 106and/or lifting gas 114 prior to utilization by hydrogen fuel cell 106can be advantageously used to, in turn, affect the operation/efficiencyof hydrogen fuel cell 106.

Referring still to FIG. 4 , in various embodiments of the presentinvention, paths 403, 402 a, 402 b and 402 c are comprised of anysuitable conduit for transferring heat including, but not limited to,pipes, heat-conductive solid structures, and the like. Additionally, invarious embodiments of the present invention, LTA craft 400 will includeboth heat exchange component 402 and component 302 described above inconjunction with FIG. 3 .

With reference next to FIG. 5 , another embodiment of the presentinvention is shown in which an LTA craft 500 includes a heat exchangecomponent 502 fluidically coupling hydrogen fuel cell 106, envelope 102,and one or both of volume of helium 206 and volume of hydrogen 204disposed within envelope 102. As stated above, a hydrogen fuel cell,such as hydrogen fuel cell 106, typically also produces heat and waterduring the exothermic process of generating electricity. In the presentembodiment, said heat exchange component provides a flow path for heat,generated by hydrogen fuel cell 106, to be provided to, and/or directlyinside of, envelope 102 to adjust the temperature of one or both ofvolume of helium 206 and volume of hydrogen 204. In the embodiment ofFIG. 5 , heat generated by hydrogen fuel cell 106 travels along path 503of heat exchange component 502 and along path 502 a of heat exchangecomponent 502 to, and/or through, envelope 102 to alter the temperatureof one or both of volume of helium 206 and volume of hydrogen 204. Itwill be understood that altering the temperature of one or both ofvolume of helium 206 and volume of hydrogen 204 can be advantageouslyused to, in turn, alter the buoyancy provided by one or both of volumeof helium 206 and volume of hydrogen 204, which may be used tocompensate for the loss of lifting force from the hydrogen consumed byfuel cell 106. In various other embodiments, heat generated by hydrogenfuel cell 106 travels along one or more of paths 502 b and 502 c (inaddition to, or in lieu of travelling along path 502 a) of heat exchangecomponent 502 to alter the temperature of hydrogen fuel cell 106 and/orhydrogen prior to utilization by hydrogen fuel cell 106. It will beunderstood that altering the temperature of hydrogen fuel cell 106and/or hydrogen prior to utilization by hydrogen fuel cell 106 can beadvantageously used to, in turn, affect the operation/efficiency ofhydrogen fuel cell 106.

Referring still to FIG. 5 , in various embodiments of the presentinvention, paths 503, 502 a, 502 b and 502 c are comprised of anysuitable conduit for transferring heat including, but not limited to,pipes, heat-conductive solid structures, and the like.

With reference next to FIG. 6 , another embodiment of the presentinvention is shown in which an LTA craft 600 includes a buoyancyadjustment feature 602 coupled with heat exchange component 402. In theembodiment of FIG. 6 , buoyancy adjustment feature selectively directsheat to one or more regions within envelope 102 to control buoyancycharacteristics of LTA craft 600. In various embodiments of the presentinvention, buoyancy adjustment feature is comprised of any suitableconduit for directing heat to one or more desired regions withinenvelope 102. It will be understood that altering the temperature of oneor regions within envelope 102 can be advantageously used to, in turn,alter the buoyancy of the one or more regions within envelope 102. Thismay be used to compensate for the loss of lifting force from thehydrogen consumed by fuel cell 106 and/or control buoyancy locally. Asan example, altering the temperature at the front or rear of LTA craft600 can be used to adjust the pitch of LTA craft 600. Likewise, alteringthe temperature at the left/port or right/starboard regions of LTA craft600 can be used to adjust the roll of LTA craft 600.

With reference next to FIG. 7 , another embodiment of the presentinvention is shown in which an LTA craft 700 includes a buoyancyadjustment feature 702 coupled with heat exchange component 502. In theembodiment of FIG. 7 , buoyancy adjustment feature selectively directsheat to one or more regions within envelope 102 to control buoyancycharacteristics of LTA craft 700. In various embodiments of the presentinvention, buoyancy adjustment feature is comprised of any suitableconduit for directing heat to one or more desired regions withinenvelope 102. It will be understood that altering the temperature of oneor regions within envelope 102 can be advantageously used to, in turn,alter the buoyancy of the one or more regions within envelope 102. As anexample, altering the temperature (of compartments) at the front or rearof LTA craft 700 can be used to adjust the pitch of LTA craft 700.Likewise, altering the temperature at the left or right regions of LTAcraft 700 can be used to adjust the roll of LTA craft 700.

With reference next to FIG. 8 , another embodiment of the presentinvention is shown in which an LTA craft 800 includes a plurality ofregions 802 a-802 f disposed within enclosure 102. In one suchembodiment, plurality of regions 802 a-802 f are at least partiallyfluidically isolated from at least one other region. Such an embodimentmitigates potential complete, and/or catastrophic, leakage of liftinggas from enclosure 102, enables improved buoyancy control, and providesfor precise adjustments to pitch, yaw and roll of LTA craft 800.Furthermore, embodiments of the present invention enable features suchas heat exchange component 402 and/or 502 of FIGS. 4 and 5 ,respectively, and buoyancy control feature 602 and/or 702, of FIGS. 6and 7 , respectively, to selectively alter the temperature of liftinggases in specific regions within enclosure 102.

With reference next to FIG. 9 , an embodiment of the present inventionis shown in which an LTA craft 900 includes a plurality of regions 902a-902 h disposed within enclosure 102. In one such embodiment, pluralityof regions 902 a-902 h are at least partially fluidically isolated fromat least one other region. Such an embodiment mitigates potentialcomplete, and/or catastrophic, leakage of lifting gas from enclosure102, enables improved buoyancy control, and provides for preciseadjustments to pitch, yaw and roll of LTA craft 900. Furthermore,embodiments of the present invention enable features such as heatexchange component 402 and/or 502 of FIGS. 4 and 5 , respectively, andbuoyancy control feature 602 and/or 702, of FIGS. 6 and 7 ,respectively, to selectively alter the temperature of, for example,helium in specific regions within enclosure 102.

With reference next to FIG. 10 , an embodiment of the present inventionis shown in which an LTA craft 1000 includes a plurality of regions 1002a-1002 c disposed within enclosure 102. In one such embodiment,plurality of regions 1002 a-1002 c are at least partially fluidicallyisolated from at least one other region. Such an embodiment mitigatespotential complete, and/or catastrophic, leakage of lifting gas fromenclosure 202, enables improved buoyancy control, and provides forprecise adjustments to pitch, yaw and roll of LTA craft 1000. Further,as with the various embodiments described above, in the embodiment ofFIG. 10 , the ratio of volume of hydrogen (in various compartments) withrespect to the surrounding volume of helium (in various compartments) isdefined such that if the entirety of the volume of hydrogen and thevolume of helium are combined to form a mixture, the mixture isnonflammable during operating conditions for LTA craft 1000.Furthermore, embodiments of the present invention enable features suchas heat exchange component 402 and/or 502 of FIGS. 4 and 5 ,respectively, and buoyancy control feature 602 and/or 702, of FIGS. 6and 7 , respectively, to selectively alter the temperature of, forexample, helium in specific regions within enclosure 102. It should benoted that although several examples of shapes, orientations andquantities of a plurality of regions are provided in FIGS. 8, 9 and 10 ,embodiments of the present invention are well suited to use with variousother shapes, orientations and quantities for the plurality of regions.

With reference now to FIG. 11 , an embodiment of the present inventionis shown in which an LTA craft 1100 includes one or more sensors shownas 1102. In the embodiment of FIG. 11 , three sensors are schematicallydepicted as 1102 a, 1102 b and 1102 c. In various embodiments of thepresent invention, one or more sensors 1102 are comprised of any ofvarious sensor types including, but not limited to, an oxygen sensor, anair sensor, a hydrogen sensor, a helium sensor, and the like. In variousembodiments of the present invention, one or more sensors 1102 are used,for example, to detect a leak (into or out of) enclosure 102, detect thepresence (or monitor the concentration level) of gases such as, forexample, hydrogen and/or helium within enclosure 102. It should be notedthat one or more sensors 1102 are also well suited for use in anembodiment as shown in any of FIGS. 1-10 .

With reference still to FIG. 11 , in one embodiment of the presentinvention LTA craft 1100 includes one or more hydrogen scavengingcomponent 1104 coupled to envelope 102. In the present embodiment,hydrogen scavenging component 1104 is configured to scavenge hydrogenpresent within enclosure 102 but which is outside of compartment 202. Inone embodiment, hydrogen scavenging component 1104 is comprised of apalladium-based getter element. It should be noted that embodiments ofthe present invention are well suited to use with any of various oftypes of hydrogen scavenging components. It should further be noted thathydrogen scavenging component 1104 can be used with or without one ormore sensors 1102, and that hydrogen scavenging component 1104 is alsowell suited for use in an embodiment as shown in any of FIGS. 1-10 .

As mentioned above, conventional cryogenic storage mechanisms for liquidhydrogen are not well suited for use in LTA craft and other aircraft.This is due, in part, to the additional weight associated withconventional cryogenic storage mechanisms for liquid hydrogen. It shouldalso be noted that the boiling point of hydrogen, at one atmosphere ofpressure, is approximately −252.8 degrees Celsius. As a result of thedifficulty of constantly keeping the liquid hydrogen sufficiently cooledbelow its boiling point, it is very likely that at least some portion ofstored liquid hydrogen will transition to a gaseous state. Thistransition from a liquid state to gaseous state is commonly referred toas “boiloff”. In certain applications the liquid hydrogen is temporarilystored without active cooling and/or without substantial additionalinsulation. In such applications, the amount of boiloff, or the rate atwhich boiloff occurs, will likely exceed the rate of boiloff found inmore heavily insulated and/or actively cooled cryogenic storagemechanisms for liquid hydrogen. In most scenarios, for example inrockets using liquid hydrogen, the boiloff is simply vented or expelledto the atmosphere and lost.

With reference now to FIG. 12 , an embodiment of the present inventionis shown in which boiloff from cryogenically stored liquid hydrogen isadvantageously captured and utilized rather than being expelled and lostas is conventionally done. With reference still to FIG. 12 , a cryogenictank 1202 is shown coupled to an intermediate tank 1204. In embodimentsof the present invention, boiloff of gaseous hydrogen from cryogenictank 1202 can be received by intermediate tank 1204. It should be notedthat embodiments of the present invention are well suited to havingintermediate tank 1204 receive all of the boiloff from cryogenic tank1202. In other embodiments of the present invention, intermediate tank1204 receives some portion of the total amount of the boiloff fromcryogenic tank 1202.

Referring now to lifting gas 114 of FIG. 12 , in one embodiment of thepresent invention, lifting gas 114 is comprised of helium and hydrogengas. As stated previously, hydrogen has long been deemed unsuitable foruse as a lifting gas in LTA craft due to the flammability of hydrogen.In the present embodiment, lifting gas 114 is comprised of a mixturewherein the percent by volume of hydrogen does not exceed approximately4 percent. As hydrogen has a lower explosive limit (LEL) ofapproximately 4 percent by volume in air, embodiments of the presentinvention advantageously provide a hydrogen-containing lifting gas whichdoes not suffer from the flammability concerns previously associatedwith conventional hydrogen lifting gases. In another embodiment, liftinggas 114 is comprised of a mixture wherein the percent by volume ofhydrogen does not exceed a percentage such that when lifting gas 114escapes to an environment where sufficient oxygen for combustion ispresent and mixes to form a local mixture, the percent by volume ofhydrogen in the local mixture does not exceed the LEL at any point. As aresult, in various embodiments of the present invention, lifting gas 114is nonflammable during operating conditions for LTA craft 1200.

As stated above, in embodiments of the present invention, LTA craft 1200comprises and optional supply line 104 which fluidically coupleshydrogen fuel cell 106 and lifting gas 114. As a result, in someembodiments of the present invention, not only does lifting gas 114provide buoyancy for LTA craft 1200, lifting gas 114 also provides asuitable hydrogen source for hydrogen fuel cell 106. In various otherembodiments of the present invention, hydrogen fuel cell 106 receiveshydrogen gas only from intermediate tank 1204 via line 1208. In variousembodiments of the present invention, the pressure within intermediatetank 1204 is controlled to meet various performance and operationcharacteristics. In one such embodiment, intermediate tank 1204 ismaintained at a pressure which enables efficient transfer of hydrogengas from intermediate tank 1204 to hydrogen fuel cell 106 via line 1208.In other embodiments, intermediate tank 1204 comprises a variable volumecontainer, e.g., a balloon, that maintains hydrogen at atmosphericpressure which may then be transferred to hydrogen fuel cell 106 via apump fluidically coupled in line 1208 and/or transferred to envelope 102via a pump fluidically coupled in line 1206. Thus, unlike manyconventional systems, embodiments of the present invention reduce orentirely eliminate the expelling and corresponding wasting of hydrogenboiloff. That is, embodiments of the present invention advantageouslycapture and utilize hydrogen boiloff.

Additionally, in various embodiments of the present invention,intermediate tank 1204 is fluidically coupled, via line 1206, with theinterior of LTA craft 1200. In such an embodiment, intermediate tank1204 is able to provide hydrogen gas boiloff, received from cryogenictank 1202, to the interior of LTA craft 1200. Thus, in such embodiments,boiloff from cryogenic tank 1202 is ultimately used to enhance, alter,or otherwise regulate the amount lifting gas within LTA craft 1200. Inone such embodiment, intermediate tank 1204 is maintained at a pressurewhich enables efficient transfer of hydrogen gas from intermediate tank1204 to the interior of LTA craft 1200 via line 1208. In various otherembodiments, the hydrogen gas boiloff from intermediate tank 1204, asreceived from cryogenic tank 1202, is used to provide hydrogen gas tohydrogen fuel cell 106 via line 1208 and to provide hydrogen gas to theinterior of LTA craft 1200 via line 1206. In other embodiments, one ormore first intermediate tanks may provide hydrogen gas to hydrogen fuelcell 106 via line 1208 and one or more second intermediate tanks mayprovide hydrogen gas to the interior of LTA craft 1200 via line 1206.

Several other advantages are realized by the various embodiments of thepresent invention. As one example, embodiments of the present inventionenable a reduced need for minimizing hydrogen boiloff (as the hydrogenboiloff is used and not wasted) resulting in less dependence upon acomplex and heavy cryogenic mechanism for the liquid hydrogen. Byreducing the need for such complex and heavy cryogenic mechanisms,embodiments of the present invention enable a lighter overall aircraft.More specifically, by capturing the hydrogen boiloff rather thanconventionally wasting or expelling hydrogen boiloff, embodiments of thepresent invention can use less insulation and/or smaller/lighter activecooling systems.

Furthermore, it should be noted that the embodiment depicted in FIG. 12can also be utilized in combination with any of the various embodimentsdescribed above in conjunction with FIGS. 1-11 . For example, thehydrogen gas boiloff from intermediate tank 1204, as received fromcryogenic tank 1202, can be used to provide hydrogen gas to the interiorof an LTA craft via line 1206 to, for example, the plurality of regions802 a-802 f of the embodiment of FIG. 8 , the plurality of regions 902a-902 h of the embodiment of FIG. 9 , and/or the plurality of regions1002 a-1002 c of the embodiment of FIG. 10 .

Referring still to FIG. 12 , and as was discussed in detail above, itshould be noted that hydrogen fuel cell 106 is comprised of any type ofhydrogen fuel cell which utilizes hydrogen and oxygen (the oxygenobtained, for example, from the surrounding air) to generateelectricity. It should further be noted, as was discussed in detailabove, that a hydrogen fuel cell, such as hydrogen fuel cell 106,typically also produces heat and water during the exothermic process ofgenerating electricity.

Referring still to LTA craft 1200 of FIG. 12 , in embodiments of thepresent invention electrical supply line 108 electrically coupleshydrogen fuel cell 106 with propulsion system 109. As stated above,although propulsion system 109 of LTA craft 100 is comprised of motor110 and propeller 112, embodiments of the present invention are wellsuited to use with a propulsion system comprised of components otherthan motor 110 and propeller 112, for example many variants of electricpropulsion including one or more of a ducted fan, ion drive, directedthrust, tilted lift system, and propeller. In various embodiments of thepresent invention, propulsion system 109 will further comprise a batteryor other electricity storage device, not shown, for storing electricitygenerated by hydrogen fuel cell 106. Hence, in some embodiments of thepresent invention, electricity generated by hydrogen fuel cell 106 isprovided to propulsion system 109 using electrical supply line 108, andthe generated electricity is used to directly power, for example, motor110 to drive propeller 112. In other embodiments, electricity generatedby hydrogen fuel cell 106 and/or stored in an electricity storage deviceis provided to electrical components of LTA craft including, forexample, air conditioning, avionics, control systems, and lighting. Insome embodiments, at the desired point in cruise the LTA craft couldconsume its own lifting gas 114 for the hydrogen fuel cell 106 and, inremoving hydrogen from envelope 102, become heavier than air, glidingdown, and using the excess H2 for additional forward thrust as describedabove.

Referring again to FIG. 12 , in various other embodiments of the presentinvention, electricity generated by hydrogen fuel cell 106 is providedto propulsion system 109, using electrical supply line 108, and thegenerated electricity is stored, for example in a battery, forsubsequent and/or simultaneous use by propulsion system 109. Suchsimultaneous use may occur, for example, during periods of greater powerdemand or need from propulsion system 109. Further, embodiments of thepresent invention are well suited to use with various combinations ofdirect/immediate use of electricity generated by hydrogen fuel cell 106and storage/deferred use of electricity generated by hydrogen fuel cell106.

With reference now to FIG. 13 , embodiments of the present invention arealso well suited to use with conventional or “heavier-than-air” craft1300. In FIG. 13 , a cryogenic tank 1302 is shown coupled to anintermediate tank 1304. In embodiments of the present invention, boiloffof gaseous hydrogen from cryogenic tank 1302 can be received byintermediate tank 1304. It should be noted that embodiments of thepresent invention are well suited to having intermediate tank 1304receive all of the boiloff from cryogenic tank 1302. In otherembodiments of the present invention, intermediate tank 1304 receivessome portion of the total amount of the boiloff from cryogenic tank1302.

Referring still to FIG. 13 , as was described in detail above inconjunction with the embodiments of FIG. 12 , in one embodiment, ahydrogen fuel cell, not shown, receives hydrogen gas from intermediatetank 1304 via a supply line, not shown. Many of the variousconfigurations and embodiments described above in conjunction with FIG.12 are similarly applicable to heavier-than-air craft 1300 of FIG. 13and are not repeated here for purposes of brevity and clarity. However,it should be noted that the embodiments of FIG. 13 , unlike manyconventional systems, reduce or entirely eliminate the expelling andcorresponding wasting of hydrogen boiloff. That is, embodiments of thepresent invention, as depicted in FIG. 13 , advantageously capture andutilize hydrogen boiloff.

Referring again to FIG. 13 , in one embodiment, heavier-than-air craft1300 will consume the captured hydrogen gas boiloff and use the capturedhydrogen gas boiloff (and a hydrogen fuel cell) to provide power toheavier-than-air craft 1300.

The foregoing Description of Embodiments is not intended to beexhaustive or to limit the embodiments to the precise form described.Instead, example embodiments in this Description of Embodiments arepresented to enable persons of skill in the art to make and useembodiments of the described subject matter. Moreover, variousembodiments have been described in various combinations. However, anytwo or more embodiments could be combined. Although some embodimentshave been described in a language specific to structural features and/ormethodological acts, it is to be understood that the subject matterdefined in the appended Claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed by way of illustration and asexample forms of implementing the Claims and their equivalents.

We claim:
 1. A hydrogen boiloff capture system comprising: a cryogenictank for storing liquid hydrogen; and an intermediate tank fluidicallycoupled with said cryogenic tank, said intermediate tank configured toreceive hydrogen gas boiloff from said cryogenic tank, said intermediatetank further configured to provide said hydrogen gas boiloff to alighter-than-air craft to regulate buoyancy of said lighter-than-aircraft, said intermediate tank configured to provide said hydrogen gasboiloff to a hydrogen fuel cell coupled to said lighter-than-air craft.2. A hydrogen boiloff capture system comprising: a cryogenic tank forstoring liquid hydrogen; and an intermediate tank fluidically coupledwith said cryogenic tank, said intermediate tank configured to receivehydrogen gas boiloff from said cryogenic tank, said intermediate tankfurther configured to provide said hydrogen gas boiloff to a hydrogenfuel cell coupled to said heavier-than-air craft.
 3. A lighter-than-aircraft comprising: an envelope; a compartment disposed with saidenvelope, said compartment containing a volume of hydrogen; a cryogenictank for storing liquid hydrogen; an intermediate tank fluidicallycoupled with said cryogenic tank, said intermediate tank configured toreceive hydrogen gas boiloff from said cryogenic tank; a hydrogen fuelcell fluidically coupled with said intermediate tank, said intermediatetank further configured to provide said hydrogen gas boiloff to saidhydrogen fuel cell, said hydrogen fuel cell configured to utilize saidhydrogen gas boiloff to generate electricity; and a propulsion systemcoupled to said envelope, said propulsion system configured to providepropulsion for said lighter-than-air craft, said propulsion systemelectrically coupled with said hydrogen fuel cell to receive saidelectricity generated by said hydrogen fuel cell, said propulsion systemconfigured to utilize said electricity in providing said propulsion tosaid lighter-than-air craft.
 4. The lighter-than-air craft of claim 3further comprising: said intermediate tank further configured to providesaid hydrogen gas boiloff to an interior of said lighter-than-air craftto regulate buoyancy of said lighter-than-air craft.
 5. Aheavier-than-air craft comprising: a cryogenic tank for storing liquidhydrogen; an intermediate tank fluidically coupled with said cryogenictank, said intermediate tank configured to receive hydrogen gas boilofffrom said cryogenic tank; a hydrogen fuel cell fluidically coupled withsaid intermediate tank, said intermediate tank further configured toprovide said hydrogen gas boiloff to said hydrogen fuel cell, saidhydrogen fuel cell configured to utilize said hydrogen gas boiloff togenerate electricity; and a propulsion system coupled to said hydrogenfuel cell, said propulsion system configured to provide propulsion forsaid heavier-than-air craft, said propulsion system configured toreceive said electricity generated by said hydrogen fuel cell, saidpropulsion system configured to utilize said electricity in providingsaid propulsion to said heavier-than-air craft.